The hitherto known electrochromic units are electrochromic windows with transparent systems, which can be coloured in any desired manner. They are intended to absorb incident electromagnetic radiation, preferably visible tight. They are e.g. used in the car sector, where they are employed in the form of dimmable rear-view mirrors. For this purpose the electrochromic windows have an electrochromic cell with two electrodes and an electrolyte located between them, the electrodes being in each case applied to a suitable carrier and at least one carrier and one electrode are transparent. The electrochromic material is applied to the transparent electrode between the electrode and the electrolyte. Glass normally forms the transparent carrier and is then coated with the transparent electrode. The electrochromic material is usually in the form of transition metal oxides, e.g. tungsten oxide. Such a window with tungsten oxide as the inorganic, electrochromic material is used in window construction, where the tungsten oxide is introduced between two window panes and is used for darkening the entire pane for reducing insolation. The electrolyte is always an ion conductor and is located between the electrochromic material, e.g. tungsten oxide, and the second electrode positioned parallel to the first. As a result of this arrangement (transparent carrier/first, transport electrode/electrochromic material/electrolyte/second electrode/carrier), it is ensured that the electrolyte and electrochromic material are always in intimate contact with one another, so that in the case of a current flow a material exchange can take place between them. As a result of an applied voltage, charges are injected into the electrochromic material, which gives rise to the desired colour change. However, it is disadvantageous that several minutes are always needed for the colouring or decolourizing of the window.
Apart from metal oxides, electrically conductive polymers are used as electrochromic materials. Here again charges are injected into the polymer by a current flow between the electrodes and give rise to a colour change. The transparent electrode is usually constituted by indium tin oxide to which the electrochromic polymer is applied. As ion conductors acidic electrolytes are needed, which is followed by the second electrode, which is usually also transparent. However, each windows have an inadequate long-term stability, because the acidic electrolytes act corrosively with respect to the transparent electrode. With time the latter gradually loses its electrical conductivity, so that the electrochromic material can no longer be activated. The electrochromic window can consequently no longer fulfil its function over a period time.
The problem of the invention is to provide an electrochromic unit of the aforementioned type, in which there is no need for a transparent carrier or a transparent electrode and which in the case of rapid switching times is characterized by a high long-term stability.